In a multi-carrier cellular mobile communication system, a terminal may transmit uplink data to a base station. Since a plurality of terminals in a single subframe may transmit uplink data, a base station transmits acknowledgement (ACK)/negative ACK (NACK) information of the uplink data to the plurality of terminals of the single subframe. For example, in a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system, ACK/NACK information of the uplink data may be referred to as a Hybrid Automatic Repeat-request (HARQ) indicator (HI). Also, a base station may transmit the HI to a plurality of terminals through a Physical Hybrid Automatic Repeat Request Indicator Channel (PHICH).
Also, a terminal may transmit a cyclic-shifted reference signal to a base station. A base station may estimate a wireless channel state of each terminal using the reference signal. Cyclic shift values of reference signals, transmitted by each of the terminals, are to be maximally spaced apart from each other to easily estimate the wireless channel.
A cyclic shift value of each terminal may be associated with a PHICH radio resource of each of the terminals. Accordingly, when the cyclic shift value of each of the terminals is determined based on only being spaced apart, a same PHICH radio resource may be assigned to each of the terminals.
When the same PHICH radio resource is assigned to each of the terminals, each of the terminals may not identify a PHICH radio resource for each of the terminals, and thereby may not receive PHICH information of data transmitted by each of the terminals.
Accordingly, a cyclic shift value of each terminal is to be maximally spaced apart from each other, and a PHICH radio resource is to be assigned to each of the terminals.